Most wines exhibit a chemical oxygen demand required for the proper development of flavors, mouthfeel and aromas. This development is termed “wine maturation”. A cap closure that allows the correct amount of oxygen into a wine bottle will promote wine maturation at an ideal rate, otherwise referred to as aging. If a cap closure has no oxygen barrier, too much oxygen will cause the wine to oxidize rapidly and shorten its shelf life. It is commonly known within the wine industry that white wines are much more sensitive to oxygen while red wines are generally more tolerant of exposure to oxygen. It is generally accepted that the proper amount of oxygen entering the wine at a proper rate through the closure will have a beneficial effect on wine quality.
The traditional closure for wine is the bark of the Quercus Suber, commonly known as cork oak. The oxygen transmission rate (OTR) of a premium natural cork is considered by many winemakers to be the gold standard. Premium wines using such corks are normally stored inverted or laid on their side. Storing wine in this manner reduces the OTR by keeping the cork wet, thus enhancing its sealing capabilities.
In the current wine industry, aluminum screw-cap closures have become a popular alternative to cork closures due to their low cost and predictable performance. The crucial sealing performance of a cap is controlled to a large extent by its liner component. Cap liners are required to seal sufficiently to prevent the beverage from leaking out of the package. They are also crucial for controlling the transmission of oxygen from the air outside the package into the product while retaining volatile flavor molecules in the beverage. Liner types have traditionally been chosen by cap manufacturers (e.g., G3), with a focus on ease of use, performance and price. It is not commonly known how to precisely select a combination of materials and their thicknesses to obtain a desired OTR over a range of OTRs.
There are two major cut-disk cap liner technologies that dominate the cap liner industry (e.g., cap liners manufactured by MEYER SEALS), those containing SARANEX™ (a polyvinylidene chloride (PVDC)/polyethylene (PE) laminate that provides barrier protection) as an oxygen barrier and those utilizing a combination of SARANEX™ with either tin or aluminum foil as the oxygen barrier. The OTR of these two cap liner designs are uniform at their respective values, the foil-SARANEX™ being much lower than the SARANEX™ alone.
The SARANEX™ layer is typically thin, ranging from 1.0 to 2.0 mils. SARANEX™ itself is normally a five layer laminate, the outermost layers being low-density polyethylene (LDPE) film with adhesive layers (e.g., ethylene-vinyl acetate (EVA)) or a similar tie-layer polymer between the LDPE and the PVDC. The PVDC is the oxygen barrier component of SARANEX. Most of the total thickness of the SARANEX™ film is due to the layers of LDPE and adhesive. The LDPE and the adhesive layers have very high OTR relative to PVDC and metal foils. The SARANEX™ cap liner is considered by some to allow too much oxygen into the wine, leading to a decreased shelf-life. The foil-SARANEX™ cap liner is known to allow almost no oxygen into the wine bottle, which can cause anaerobic conditions resulting in reduced or sulfidic aromas. Therefore, some in the wine industry believe that foil-SARANEX™ liners allow in too little oxygen. OTR tests of inverted natural premium Flor grade corks using the OX-TRAN (a system for oxygen transmission rate testing) system from MOCON (a provider for oxygen permeation detection instruments) determined that their OTR values were between those of SARANEX™ and foil-SARANEX™ cap liners.
There are currently no commercial cap liners for wine screw caps that provide OTR values close to that of a premium inverted natural bark cork. One prior attempt to create this range of OTR values was made by producing liners using different thickness of ethylene vinyl alcohol (EVOH) in place of the SARANEX™ barrier. However, the OTR of three thicknesses of EVOH were virtually identical to each other and very close to the OTR of a SARANEX™ cap liner. Another prior attempt was made using perforated metalized polymer, which resulted in unacceptable variability in OTR values.
Another prior attempt to achieve the desired OTR included applying various perforation schemes through tin foil and then using the perforated foil to create a laminate liner similar to a foil-SARANEX™ liner. However, this produced neither the desired control of OTR, nor an OTR close to that of a wine package finished with a premium natural bark cork. The perforations in the foil, which may be known as the primary barrier, did not control the OTR. The OTR values of this configuration were similar to that of a foil-SARANEX™ liner without perforations in the tin foil.